GPS World, September 2014

Algorithms Methods INNOVATION FIGURE 6 Aerial view of the forested site RN86 around the GPS antenna marked with a circle independent nearly co located in situ measurements We also compared the GPS estimates to the nearest SNOTEL station SNOTEL from snowpack telemetry is an automated system for collecting snowpack and related data in the western U S operated by the U S Department of Agriculture Although not co located with GPS SNOTEL data are important because they provide accurate information on the timing of snowfall events The three sites we used were 1 a site in the T W Daniel Experimental Forest within the Wasatch Cache National Forest in the Bear River Range of northeastern Utah with an elevation of 2600 meters 2 one of the stations of the EarthScope Plate Boundary Observatory a grassland site located near Island Park Idaho and 3 an alpine site in the Niwot Ridge Longterm Ecological Research Site near Boulder Colorado While we have fully documented the results from each site due to space limitations we will only discuss the results from the forested site known as RN86 in this article This is a more challenging site than the other two due to the presence of nearby trees Furthermore it was subject to denser in situ sampling of 20 150 measurements spatially replicated around the GPS antenna and repeated approximately every other week for about one year We show results for the 2012 wateryear the period starting October 1 through September 30 of the following year Where GPS site RN86 was installed topographical slopes range from 25 to 65 at the 2 meter spatial scale with average of 5 within a 50 meter radius around the GPS antenna RN86 was speci cally built to study the impact of trees on GPS snow depth retrievals see FIGURE 6 Ground crews manually collected in situ measurements around the GPS antenna approximately every other week starting in November 2011 Measurements were made every 1 2 meters from the antenna up to a distance of 25 30 meters In the second half of the year the sampling protocol was changed to azimuths of 0 N 45 NE 135 SE 180 S 225 SW and 315 NW With these data it is possible to obtain in situ average estimates with their own uncertainties based on the number of measurements which allows a more meaningful comparison There is reduced visibility at the www gpsworld com September 2014 GPS World 49

View the Covers and the Table of Contents pages from every issue of this publication, all gathered together for easy browsing. Just flip pages and zoom as you normally do to see each issue's Cover and Table of Contents, then follow links directly to interesting content.